When assigning function to object inside another function, what really happens in javascript?

Question

Look at this code for example:

var arr = [];

var assignFunction = function() {
  for (var i = 0; i < 3; i++) {
    arr[i] = function() {
      console.log(i);
    }

  }
}

arr[0];
arr[1];
arr[2];

You would expect it will assign a function that you can call/run, but its not. I'm looking for good explanation what its really doing. arr[i] is typeof function, meaning it is being assigned, but will never run and print anything to console.

What do you mean "it's not"? That function is certainly runnable. You just don't run it. — Sergio Tulentsev, Nov 10 '17 at 08:25
`arr[0]` is function, just like `assignFunction` is a function. `arr[0]()` will run this function, just like `assignFunction()` will run _that_ function. — Amadan, Nov 10 '17 at 08:26
And then he will have problem with closures.It will display 3 by 3 times. — Mihai Alexandru-Ionut, Nov 10 '17 at 08:26
@Alexandru-IonutMihai: yes, that we have :) But it's not very relevant. Probably will be their next question (which will be dup-closed within a minute) — Sergio Tulentsev, Nov 10 '17 at 08:27
`arr[0]` is an object of type `Function`. You can call it the same way you call any function: `arr[0]()`. — axiac, Nov 10 '17 at 09:04

score 0 · Answer 1 · answered Nov 10 '17 at 09:02

The "Problem"

You need to call assignFunction to assign the functions to the indices off arr. After that you can execute a function with arr[index]().

why each function prints 3 in the console, you can read in this answer

Working Example

var arr = []

var assignFunction = function() {
  for (var i = 0; i < 3; i++) {
    arr[i] = function() {
      console.log(i)
    }
  }
}

assignFunction()

arr[0]()
arr[1]()
arr[2]()

When assigning function to object inside another function, what really happens in javascript?

1 Answers1

The "Problem"

Working Example